| 摘要 |
The subject of the present invention is to provide a drilling tool for further improving the hole position precision and loss endurance capability. To solve the problem, there are two cutting blades (2) formed on a front end of a tool body (1), and two spiral chip removal grooves (3a, 3b) are formed on a periphery of the tool body (1) and continuously arranged on a middle part. Each of the chip removal grooves (3a, 3b) is made by the drilling tool arranged in parallel with a joint part to have a total length equal to 20% to 55% of the circumference length of the circle with a tool diameter in a circumferential direction facing the axial direction from the front end of the tool by taking a range edge (4) smaller than one multiple of the tool diameter. A hard leather film (5) arranged on an outer circumference surface of the tool is provided with a thickness equal to 0.5 <mu>m to 10 <mu>m facing the axial direction from the front end of the tool by taking a range smaller than one multiple of the tool diameter. The hard leather film (5) is arranged to be thicker at further front side of the tool. The tool has a core thickness (W) which is equal to 20% to 60% of the tool diameter. |
